Multiwell plates are used extensively in molecular biology laboratories and elsewhere. One such use is in Polymerase Chain Reaction (PCR) experiments where, once filled or part filled with reagents, the plates are often sealed prior to further processing.
Multiwell plates now come in a variety of formats. 96 wells, in a 12.times.8 array, is one standard but now a 384 well format is becoming increasingly common. Forming a cheap, re-usable seal on these 384 plates presents a real problem.
There are a number of known ways of achieving such seals. For example, a foil or plastic film may be applied across the entire upper surface of the plate. Thus heat sealable aluminium foils or adhesive plastic films are commercially available. Once applied, these films provide an efficient, gas and liquid tight seal but are tiresome to apply and remove. Access to each well can only be obtained by piercing the film or by peeling the film off by hand or with a foil stripper. Consequently, this type of seal is not re-usable, and is not suitable for robotic application or removal.
Alternatively, a seal may be achieved by placing a relatively heavy, flexible rubber mat over the entire surface of the plate. The weight of the mat and any plates stacked on top of the mat keep the seal in place. It is important that the mat does not slide over the top of the plate in order to avoid cross-contamination. In the case of 96 well plates, this is achieved by having 96 raised pimples or "dimples" on the surface of the mat in an array which matches exactly the array of wells. Each dimple is sized and shaped to sit firmly into a well. Once in place, no lateral movement of the mat is possible because the perimeter of each dimple fits snugly within its respective well.
This arrangement is not applicable to the 384 well version because the wells are much smaller in diameter. Each dimple would need to be so small in profile that it becomes very difficult to align the mat with the wells. Even if the mat can be aligned, there is an increased tendency for the mat to slide across the top face of the wells because each dimple is correspondingly smaller than in the 96 well version.
As a further alternative, sealing caps can be applied, either in strips or as an array of 96. These sealing caps consist of individual, circular cylindrical walled caps with a pierceable lid. They fit snugly into the internal bore of each plate and each cap normally has an outer lip, which prevents it entering into the well beyond a certain point.
These caps are time-consuming to apply and require a good deal of manual dexterity on the part of the technician. Furthermore, sealing caps would be practically impossible to fit to 384 well plates, and, in any event, cannot be inserted or removed robotically.
It is therefore an objective of the present invention to overcome some or all of these disadvantages and provide an improved, re-usable sealing means applicable to all multiwell plates.